A memorial service has been held on Australia's Christmas Island for the victims of boat sinking that left at least 30 people dead.

The private service was attended by the survivors, immigration officials and a local Islamic leader, the immigration department said.

Further services are planned this week for the victims of Wednesday's accident, which was survived by 42 people. Rescuers recovered the bodies of 30 men, women and children from the ocean.

Australian federal police superintendent Gavan Ryan said about 15 bodies have been identified so far by surviving family members and friends who were either on the boat or were already in the island's detention centre.

Officials say the boat could have held up to 100 Iraqi, Iranian and Kurdish passengers.Mr Ryan said he believed more bodies could be in underwater caves near where the boat broke up on rocks off Christmas Island. "We are hoping by the end of tomorrow to have a definite answer of how many people are missing," he said.

The tragedy has once again put the spotlight on the three-year-old Labour government's struggle to come up with an effective refugee policy. Critics on both sides say the current approach encourages asylum seekers to undertake perilous sea journeys.

Opposition leader Tony Abbott called for the government to return to tougher refugee laws that he said would keep the boats from coming to Australia."It is important that we put policies in place as quickly as humanly possible that do offer the prospect of stopping the boats," he told reporters in Sydney.

In recent years, many asylum seekers have come from Afghanistan, Iran, Iraq and Burma. Generally, they first fly to Indonesia and then continue on to Australia by sea, often in small, rickety fishing boats with few provisions and no safety gear.